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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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    <script>
        function User(name, age) {
            this.name = name;
            this.age = age;
            
        }
        // 每个构造中都有一个原型对象
        // 只要是对象就会有一个__proto__
        console.log(User.prototype.__proto__)   // Object
        console.log(User.prototype.__proto__.prototype)   // null
    </script>
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